External Hard Drive encryption question

This is actually a followup up to the thread "unencrypt ext drive permanently," but is slightly different.

I have a external LaCie Quandra 4tb that formerly had a sparse image on it. I moved all files from the sparse image to the parent hard drive, then deleted the sparse image.

Just a quick question to be sure here. I am able to encrypt the drive now without the risk of losing the files, correct?
Will this take a long time? There are just under 2 Tb on the external.

TIA
John
PS...I found that the sparse image is only dynamic on the way up, ie it can expand to accommodate new files added, but will not shrink as items are moved/deleted so that what had grown to 2.3 Tb's stayed that way even though nearly all of the files were moved away and no longer showed up in the finder under the sparse image.

PS...I found that the sparse image is only dynamic on the way up, ie it can expand to accommodate new files added, but will not shrink as items are moved/deleted so that what had grown to 2.3 Tb's stayed that way even though nearly all of the files were moved away and no longer showed up in the finder under the sparse image.

Click to expand...

This is correct. You can run the command below in Terminal to shrink the image down to what it should be. Substitute the real path and name.

A followup...
External drive now encrypted. When the machine boots a box comes up asking for the password for the encrypted drive.
two things
if I choose to unencrypt using the password, when I later eject the drive, and choose to mount it again using disk utility, it remounts unencrypted, ie, no password requested...is this correct?

If during boot I choose "cancel" from the password request box, and later go to disk utility to mount it, the menu item there is "unlock," when, if clicked, the password box comes up and with entry, the disk mounts.

Where I am going with this is: Once the external is mounted and then ejected, is there a way to "lock" it thus requiring the password again to mount it? Something like an Eject and Lock command?

Staff Member

A followup...
External drive now encrypted. When the machine boots a box comes up asking for the password for the encrypted drive.
two things
if I choose to unencrypt using the password, when I later eject the drive, and choose to mount it again using disk utility, it remounts unencrypted, ie, no password requested...is this correct?

If during boot I choose "cancel" from the password request box, and later go to disk utility to mount it, the menu item there is "unlock," when, if clicked, the password box comes up and with entry, the disk mounts.

Where I am going with this is: Once the external is mounted and then ejected, is there a way to "lock" it thus requiring the password again to mount it? Something like an Eject and Lock command?

Thanks again

Click to expand...

When you boot or attach the drive and that prompt comes up, you are not unencrypting, you are just unlocking the drive same as it you did that in Disk Util.

Whenever you eject or unmount that drive it is always still encrypted and it is "locked" again. Does that make sense?

It appears "locking" and "Mounting" are two different things? It seems UN locking requires entry of the password, while mounting requires just a click?

I think what I am looking for is a way to make that drive visible and invisible in finder, and when it is desired to make it visible to require the password, essentially a password protection for it. I suppose I am looking for a way to lock and unlock on the fly.

I have that now, in a sense, but it requires a power down/up of the drive or the computer. I would like to be able to do it without that. Maybe it can't be done the way I want. What I have though is close to want I want, just not quite there yet.

Staff Member

I think what I am looking for is a way to make that drive visible and invisible in finder, and when it is desired to make it visible to require the password, essentially a password protection for it. I suppose I am looking for a way to lock and unlock on the fly.

Click to expand...

You can do what you want from Disk Util and is should work like what you want.

I am on Yosemite, but from memory I think it worked the same in Mavericks.

If you eject the disk from the Desktop you will still see the volume shaded out in Disk Util. If you double click that shaded area it will ask for the password. There is a checkbox there to remember the PW in keychain, and to get what you want you need to leave that unchecked. If you have it checked, it will mount without asking for the PW since it is already stored in Keychain.

If yours is mounting without a PW, you may have saved it in Keychain and you can just remove that Keychain entry to get the prompt again.

It is, I think, as Alrescha states. May have been changed in Yosemite, but in Mav 10.9.5 :

If "cancel" was chosen on boot (instead of entering the password), the disk is there but greyed and the item in disk util is labeled "unlock" and if clicked, the password is requested.

However, once that password is entered, the only choices seem to be mount and unmount and no password is involved.

My system took a hit in performance going to Mavericks, so Yosemite is not in the cards for me with this machine, so I'll live with it. Just wanted to be sure there wasn't something I was missing.
Many thanks for the patience and help on this

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